Lymphoreticular and Hematopoetic Infections
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Bacillary Angiomatosis

General Goal: To know the major cause(s) of bacillary angiomatosis, how it is transmitted, and the major manifestations of the disease.

Specific Educational Objectives: The student should be able to:

1. describe the common means of transmission of this diseases.

3. describe the major manifestations of this disease.

4. describe the clinical case definition of Bacillary Angiomatosis.

4. describe how you diagnose, treat and prevent this disease.

Reading: MEDICAL MICROBIOLOGY by P.R. Murray, K.S. Rosenthal, and M.A. Pfaller, 6th Edition. p. 371.

Lecture: Dr. Neal R. Chamberlain

Overview

Bacillary angiomatosis is a systemic disease diagnosed in immunocompromised patients; it results in numerous subcutaneous nodules and is characterized by vascular proliferation. These nodules have also been observed postmortem in the larynx, gastrointestinal tract, peritoneum, and diaphragm. Bacillary angiomatosis is classified as a category B condition in HIV-infected patients.

Etiology

B henselae and B quintana cause bacillary angiomatosis.

Manifestations

Nearly all cases of bacillary angiomatosis are seen in immunocompromised patients, with most cases reported in patients with AIDS. Immunocompetent persons can also develop the disease, but it is rare.

Patients with bacillary angiomatosis usually report having scattered cutaneous papules and nodules or a subcutaneous nodule resembling a common bacterial abscess. Some of the nodules can be rather large (up to 10 cm in diameter). Patients may have only one lesion or hundreds of lesions. The four different skin lesions seen in this disease are (1) globular angiomatous papules or nodules resembling pyogenic granuloma, (2) violaceous nodules resembling Kaposi sarcoma, (3) a lichenoid violaceous plaque, or (4) a subcutaneous nodule with or without ulceration.

Because the disease can cause pathology in other parts of the body besides the skin, a patient may have weight loss and lymphadenopathy. B henselae can also infect the liver causing hepatica peliosis, which results in nausea, vomiting, diarrhea, and fever with hepatosplenomegaly.

Epidemiology

About 50% of patients with bacillary angiomatosis are infected with B henselae, and the remaining cases are infections caused by B quintana.
The disease is primarily seen in immunocompromised patients, predominately AIDS patients with CD4 cell counts below 200.
An important means of transmitting disease to humans when bacillary angiomatosis is due to B henselae and B quintana is by association with flea-infested cats (Ctenocephalides felis). The cat acquires the organism from a flea that carries B henselae or B quintana and then transmits the organism to humans when they bite or scratch.
B quintana can also be transmitted to humans by the body louse Pediculus humanus.

Pathogenesis

Trauma to the dermis associated with a cat bite of scratch can expose an individual to B henselae or B quintana. B quintana can also be transmitted to humans by body lice. Once in the dermis Bartonella will be phagocytized by macrophages and taken to the regional lymph nodes. Bartonella are contained within the regional lymph nodes of immunocompetent patients. If symptomatic, patients will manifest signs and symptoms of classic cat-scratch disease (see in phagocyte section of handout). However, immunocompromised individuals are unable to contain the bacteria, and Bartonella will enter the bloodstream and infect endothelial cells throughout the body. The infected endothelial cells produce monocyte-macrophage chemoattractant protein 1 (MCP-1), which attracts macrophages to the site of infection. The macrophages are activated at the site of endothelial cell infection to secrete vascular endothelial growth factor (VEGF) and other endothelial cell mitogens to induce vascular proliferation. The Bartonella infected endothelial cells will upregulate proangiogenic factors, inhibit apoptosis through inhibition of caspases, and upregulate adhesion molecules, which promote vascular proliferation as well.

Diagnosis

A physical examination of the patient for the characteristic lesions and biopsy of the lesions helps to confirm the diagnosis of bacillary angiomatosis. Hematoxylin and eosin (H&E) stained slides contain sections with many blood vessels of varying dimensions lined by swollen endothelial cells that contain bacilli. The bacteria can be stained more clearly with Warthin-Starry silver stain. Infiltrates of acute and chronic inflammatory cells as well as fibrin deposits may also be seen.

Therapy and Prevention

Treatment of patients who have bacillar angiomatosis with oral erythromycin for 3 months usually results in the skin lesions gradually fading. Disposal of the cat is not recommended since it will carry the bacillus for only a limited period of time; declawing appears to make no difference in cat to human transmission rates. Flea-control measures should be undertaken on a regular basis. Immunocompromised patients who are considering getting a cat should get an adult indoor cat of known origin rather than a young kitten.

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